This invention relates to starters of internal speed reduction type and, more particularly, to improvements in a buffering mechanism of a starter in which incorporating a planetary speed reduction mechanism.
A prior art speed reduction mechanism of the type mentioned is shown in FIGS. 1 and 2. The mechanism comprises a DC motor 1, which includes an armature 2, a pole member 3 constituted by a permanent magnet material for magnetically energizing the armature, a yoke 4 carrying the pole 3 mounted on the inner periphery. A rotary shaft 5 of the armature 2 is supported in a bearing 7, which is mounted on the inner periphery of an intermediate bracket 6 which is in turn fitted in socket 4a of the yoke 4. The rotary shaft 5 has an extension, on which a spur gear 8 is formed. An output shaft 9 is supported via a sleeve bearing 10 on the extension of the rotary shaft 5. Planetary gears 11 are coupled between the spur gear 8 and an internal ring gear 12 which is fittedly secured to the socket 4a of the yoke 4. Each planetary gear 11 is supported on a bearing 14, which is in turn fitted on a pin 13 extending from a flange 9a formed at the end of the output shaft 9. These planetary gears 11 execute planetary motion. The ring gear 12 is formed on the outer periphery with grooves 12b, and projections projecting from the inner periphery of the yoke 4 are received in the grooves 12a, thus receiving the reaction force against the motion of the planetary gears.
In operation, the armature 2 is energized from a battery (not shown) to produce a torque in a magnetic field produced by the pole member 3. This torque is transmitted through the spur gear 8 on the shaft 5 to the planetary gears 11. Thus, a motion of the planetary gears 11 is produced, causing rotation of the pins 13 in the direction of rotation of the spur gear 8. This torque is transmitted to the output shaft 9 via the flange 9a. With the motion of the planetary gears, a reaction force against the torque is produced in the ring gear 12. The reaction force is transmitted through the projections 4a, which are in engagement with the grooves 12a in the peripheral direction, to the yoke 4 and received by the same. The torque of the output shaft 9 is transmitted through a pinion (not shown), which is mounted on the force end of the shaft 9, to a ring gear (not shown) in an internal combustion engine.
The prior art starter described above is not provided with any mechanism for buffering an impact load exerted to the power transmission mechanism section. Therefore, it is difficult to obtain sufficient reliability with respect to a comparatively high load. In addition, the speed reduction mechanism as described above has a short life.